[Sema] Move predates concurrency remarks to warnings

include/swift/AST/DiagnosticsSema.def

@@ -2538,11 +2538,11 @@ NOTE(add_nominal_sendable_conformance,none,
 NOTE(add_generic_parameter_sendable_conformance,none,
      "consider making generic parameter %0 conform to the 'Sendable' protocol",
      (Type))
-REMARK(add_predates_concurrency_import,none,
+WARNING(add_predates_concurrency_import,none,
      "add '@preconcurrency' to %select{suppress|treat}0 "
      "'Sendable'-related %select{warnings|errors}0 from module %1"
      "%select{| as warnings}0", (bool, Identifier))
-REMARK(remove_predates_concurrency_import,none,
+WARNING(remove_predates_concurrency_import,none,
      "'@preconcurrency' attribute on module %0 is unused", (Identifier))
 WARNING(remove_public_import,none,
         "public import of %0 was not used in public declarations or inlinable code",

test/ClangImporter/objc_async.swift

@@ -6,7 +6,7 @@
 
 import Foundation
 import ObjCConcurrency
-// expected-remark@-1{{add '@preconcurrency' to suppress 'Sendable'-related warnings from module 'ObjCConcurrency'}}
+// expected-warning@-1{{add '@preconcurrency' to suppress 'Sendable'-related warnings from module 'ObjCConcurrency'}}
 
 @available(SwiftStdlib 5.5, *)
 @MainActor func onlyOnMainActor() { }

test/Concurrency/actor_isolation.swift

@@ -8,7 +8,7 @@
 // REQUIRES: concurrency
 // REQUIRES: asserts
 
-import OtherActors // expected-remark{{add '@preconcurrency' to suppress 'Sendable'-related warnings from module 'OtherActors'}}{{1-1=@preconcurrency }}
+import OtherActors // expected-warning{{add '@preconcurrency' to suppress 'Sendable'-related warnings from module 'OtherActors'}}{{1-1=@preconcurrency }}
 
 let immutableGlobal: String = "hello"
 var mutableGlobal: String = "can't touch this" // expected-note 5{{var declared here}}

test/Concurrency/global_actor_serialized.swift

@@ -11,7 +11,7 @@
 // a global-actor annotation that is an error in Swift 6, but only a warning
 // in Swift 5, then we do not reject the import as an error.
 
-import SerializedStruct // expected-remark {{add '@preconcurrency' to treat 'Sendable'-related errors from module 'SerializedStruct' as warnings}}
+import SerializedStruct // expected-warning {{add '@preconcurrency' to treat 'Sendable'-related errors from module 'SerializedStruct' as warnings}}
 
 // use it to force the right checks happen.
 func test() async -> Int {

test/Concurrency/predates_concurrency_import.swift

@@ -14,7 +14,7 @@
 @preconcurrency import NonStrictModule
 @_predatesConcurrency import StrictModule // expected-warning{{'@_predatesConcurrency' has been renamed to '@preconcurrency'}}
 @preconcurrency import OtherActors
-// expected-remark@-1{{'@preconcurrency' attribute on module 'OtherActors' is unused}}{{1-17=}}
+// expected-warning@-1{{'@preconcurrency' attribute on module 'OtherActors' is unused}}{{1-17=}}
 
 func acceptSendable<T: Sendable>(_: T) { }
 

test/Concurrency/sendable_without_preconcurrency_2.swift

@@ -9,7 +9,7 @@
 // REQUIRES: asserts
 
 import StrictModule // no remark: we never recommend @preconcurrency due to an explicitly non-Sendable (via -warn-concurrency) type
-import NonStrictModule // expected-remark{{add '@preconcurrency' to suppress 'Sendable'-related warnings from module 'NonStrictModule'}}
+import NonStrictModule // expected-warning{{add '@preconcurrency' to suppress 'Sendable'-related warnings from module 'NonStrictModule'}}
 
 actor A {
   func f() -> [StrictStruct: NonStrictClass] { [:] }

test/Concurrency/voucher_propagation.swift

@@ -15,7 +15,7 @@
 // REQUIRES: OS=macosx
 
 import Darwin
-import Dispatch // expected-remark {{add '@preconcurrency' to suppress 'Sendable'-related warnings from module 'Dispatch'}}
+import Dispatch // expected-warning {{add '@preconcurrency' to suppress 'Sendable'-related warnings from module 'Dispatch'}}
 import StdlibUnittest
 
 // These are an attempt to simulate some kind of async work, and the